The several commercially known versions of self-service automobile washing systems fall into two basic categories, both involving in common the pressurized issuance of a cleaning fluid from a portable user-held spray wand.
In one type of system, the portable unit is without valving, being simply a passive issuance device. The valving of cleaning fluid is effected by a valve located remotely from the portable unit, such as at the fixedly located pressurized source of the cleaning fluid. such valve may be controlled by a timing unit, or by an electrical switch and associated electrical conductors connecting the portable unit to the valve. A disadvantage of this system type is the undesired presence of electrical energy and necessary electrical insulation in the portable unit. A further shortcoming is that there is not an automatic turn-off feature in the portable unit, i.e., should the user drop the unit, cleaning fluid issuance continues.
In the other type of system, the portable unit includes a valve, typically not of electrical variety and having a spring-loaded user controlled operating stem. This type of system has clear advantage over that discussed above in several respects. Thus, no electrical energy is present in the portable unit and, upon a user dropping the portable unit, it self-deactivates. Such advantages are gained, however, at the cost of structural complexity of the portable unit, in respect of both the presence of the valve therein and such spring-loading mechanism therewith.